The present invention relates to hermetic sealing, and in particular to semi-rigid, deflectable closures for sealing containers.
A variety of methods are in use in the canning, preserving, and food processing field, both in industry and in the home, for closing and hermetically sealing containers, such as Mason jars. The advantages and disadvantages of any particular sealing method are determined by such factors as the cost of the containers and closures, the nature of the product to be canned, convenience to the users, and economies achieved by mass production. The advantages and disadvantages of a number of these methods are discussed below.
One early method employed a metal screw cap having a porecelain inner linear adapted to be used with a thin, flat annular rubber gasket to seal the mouth of the conventional Mason jar. After sterilization, the annular rubber gasket is placed on the sealing rim of the jar to be sealed. The metal cap is screwed tight and then turned back about one-quarter of a turn. The container and its contents are then processed, using either steam pressure or boiling water in the conventional manner depending in part on the product to be canned. During the processing cycle, the hot gases formed within the container are vented over the gasket and out under the cap. Immediately after processing and while the container and its contents remain hot, the metal screw cap is firmly tightened upon the rubber gasket to form the hermetic seal.
This technique has a number of disadvantages, foremost of which is the high cost of the metal screw caps, which are usually plated or zinc-lined. Additionally, the poreclain liners are susceptible to breakage, as well as to separation of the liners from the cap.
Related to the above canning method is the use of glass disk closures together with annular rubber gaskets for sealing non-threaded jars which have toggle-acting wire clamps. After sterilization, the rubber gasket is placed upon the sealing rim of the jar and the solid glass closure is placed over the open mouth of the jar and upon the gasket. The wire clamp is positioned in place but not locked. Immediately after processing and venting, the wire clamp is pressed down into its locked position, thereby applying compressive force upon the rubber gasket to achieve hermetic sealing.
The disadvantages of the glass disk closures are their high cost, their susceptibility to breakage, and the requirement of special wire clamp jars.
Another technique is the plated screw cap with a plastic annular inner liner or ridge. This cap is adapted to be tightly screwed into position over the mouth of the container to achieve a pressure sealing contact with the rim of the container. The processing and venting procedure is the same as described above with the early porcelain lined caps, and the plastic annular liner must be hermetically sealed to the inside of the cap if an acceptable seal is to be achieved. The advantage of this sealing method is the ease of reclosing the container after the original seal has been broken to provide portection for a limited period of time to the contents of the container until such contents are consumed. The relatively low cost of these plastic lined caps justifies their disposed after use and their re-use generally is not recommended due to degradation of the liner.
In the canning of certain types of products, where the item has a natural immunity to spoilage or has been treated to resist deterioration, metal screw caps with coated cardboard inserts are used. While the seal between the cardboard insert and the rim of the jar may not be entirely secure over a long period of time, its low cost makes this technique attractive. This apparatus is not acceptable for canning.
A related technique is the use of a thin, non-porous paper which is placed over the open mouth of and cemented to the rim of the container. A metal screw cap placed over the sealed container protects the thin paper closure. The low cost of this technique for sealing certain products accounts for its wide popularity, but again it is not suitable for canning.
A widely used method of canning in the food processing industry employs the self-sealing, metal lid with an annular inner sealant or adhesive. The acceptance of this technique is based upon its low cost and upon the ease by which the container may be hermetically sealed in an automatic or semi-automatic fashion during the normal processing cycle. The metal lid is formed as a thin disk having a slightly rolled edge adapted to surround the open mouth of the container adjacent the rim to prevent lateral movement of the lid. A ring of heat-sensitive sealant or adhesive is applied to the inner surface of the metal lid adjacent its perimeter to provide for a sealing contact with the rim of the container. The cleaned metal lid is placed upon the jar to be sealed and a screw band or annular clamp is fastened in place. The jar with its contents is then processed in the conventional manner. After processing, the sealed jar is left to stand overnight. By virtue of the slow cooling of the jar and its contents, the pressure reduces within the jar causing the lid to be retained against the rim and the hermetic seal to be maintained. After the jar has cooled, the screw band may be removed.
While the cost is relatively low, a number of disadvantages exist with this method. First, by virtue of the use of a heat-sensitive sealant, normal venting can occasionally cause improper radial movement of the sealant at unpredicatable locations around the lid resulting in tiny cracks which may not fully close during the cooling cycle as the pressure within the container reduces. Since the sealant functions as an adhesive, the lid is held tightly in place even though a hermetic seal may not have been achieved. Secondly, the stiffness of the metal lid is such that very little depression of its center portion occurs even with proper hermetic sealing, and visual inspection of the lid may not reveal the condition of the seal. In addition, once the central portion of the metal lid has become depressed, it tends to set and retain its shape whether or not a hermetic seal is maintained. Finally, the metal lid, even though plated, is frequently found to have oxidized leaving traces of contaminant upon the inner surface of the lid.
With the canning methods described above, the undamaged glass containers, glass disk closures, and heavy metal screw caps with porcelain liners may be reused. However, the annular rubber gaskets, the plasticized metal screw caps and the adhesive-sealing lids are discarded after use. The coated cardboard inserts and the cemented non-porous paper closures mentioned above are destroyed when the seal is broken. Each of these methods possesses the inherent disadvantage that not all of the structural elements needed for acceptable sealing are reusable.
Another universal disadvantage with these prior art sealing methods is the lack of a quick, simple, and reliable method of determining whether or not an acceptable hermetic seal has been achieved and will be maintained. The usual procedure of immersion in water after a suitable waiting period to test for air-leaks is time-consuming and costly. In addition the closures mentioned are burdened by the high cost of manufacturing.
It is a principal object of the present invention to provide an improved lid for sealing containers that is comprised of non-porous, non-corrosive and rust-free material which may be extensively reused, will provide a visual indication of the existence of a hermetic seal, and is inexpensive to manufacture.